1. Field of the Invention
The invention relates to electrical generators and motors and, more particularly, electrical generators and motors with counter-rotatable rotors.
2. Description of Related Art
Aircraft systems are increasingly being designed to accommodate greater and greater electrical loads as are other applications for generating electricity. Electrical power is extracted mechanically from the engines that power aircraft as well as other vehicles. When operating an aircraft engine at relatively low power levels, e.g., while idly descending from altitude, extracting electrical power from the engine mechanical power may reduce the ability to operate the engine properly. Current turbofan aircraft gas turbine engines requiring higher demands for aircraft power utilize very large generators mounted to a core engine driven gearbox. At flight conditions where lower thrust is required but high electric power such as approach, the core engine must run fast to keep up the demand but the resultant is more thrust which must be spoiled to maintain approach speeds thus reducing fuel efficiency.
Electrical power may be extracted from the high-pressure (HP) engine spool in a gas turbine engine. The relatively high operating speed of the HP engine spool makes it an ideal source of mechanical power to drive the electrical generators connected to the engine. However, it is desirable to draw power from other sources within the engine, rather than to rely solely on the HP engine spool to drive the electrical generators. The low-pressure (LP) engine spool provides an alternate source of power transfer, however, the relatively lower speed of the LP engine spool typically requires the use of a gearbox, as slow-speed electrical generators are often larger than similarly rated electrical generators operating at higher speeds. Electrical generators operating off the LP rotor or spool require large generators due to low speeds of the LP rotor or gearboxes to increase speed. These generators are a simple rotor and stator configuration.
Therefore, there is a need for an electrical generator for aircraft turbofan gas turbine and other engines that can be used to provide a great amount of electrical power over a wide range of engine operating speeds.